Robert Caldwell was gunned down Aug. 15 in Riverside, Ohio near Dayton. Six people, including his ex-wife and his former in-laws from Burlington, Kentucky, have been indicted in connection with his death.

The man's 14-year-old son is still missing, officials said. Jacob Caldwell has not been seen following his father's death.

The U.S. Attorney's Office has accused Sterling Roberts, 34, of Spartanburg, South Carolina, and the victim's ex-wife Tawnney Caldwell, 33, of murder.

Tawnney Caldwell's mother and step-father live in Burlington, Kentucky, officials said. James Harmon, 55, and Chandra Harmon, 54, are charged with aiding and abetting Sterling Roberts' illegal gun possession. Sterling Roberts had previously been convicted of burglary and drug charges in Montgomery County, Ohio, according to court documents.

Among the other charged in Robert Caldwell's death are Chance Deakin, 25, and Christopher Roberts, 30. Christopher Roberts is Sterling Roberts' brother, while Chance Deakin is his half-brother. They have been charged with aiding and abetting their brother's gun possession.

Tawnney Caldwell and Chandra Harmon are also accused of conspiring to intimidate and threaten witnesses in November 2017 after Robert Caldwell was killed.

Sterling Roberts is in jail in South Carolina on other charges. The remaining suspects were all arrested Feb. 28.

Prosecutors have not revealed a motive in the case.

According to his obituary, Robert Caldwell had remarried and had five children.

The U.S. Attorney's Office said the missing 14-year-old and two other children belonged to Robert Caldwell and Tawnney Caldwell. Officials said two other children from that relationship are being cared for by Robert Caldwell's family.

The FBI is offering a $15,000 reward for information leading to the recovery Jacob Caldwell and the arrest and conviction of anyone involved in his disappearance.